Device and method for heating using rf energy

ABSTRACT

A method of heating and/or thawing using an RF heater is described. In some cases the heating differentially heats portions according to their dissipation ratios. Optionally, this avoids dissipating large amounts of energy into thawed portions while frozen portions are still extant and heat slowly. Optionally, this prevents overheating of thawed portions.

RELATED APPLICATIONS

The present application claims the benefit under 119(e) of U.S.Provisional Patent Application No. 61/193,248 filed 10 Nov. 2008 andU.S. Provisional Patent Application No. 61/253,893 filed 22 Oct. 2009and is related to two PCT applications Agent References: 46672 and 47574filed on 10 Nov. 2009, the disclosures of which are incorporated hereinby reference.

FIELD OF THE INVENTION

The present application, in some embodiments thereof, is concernedgenerally with dissipation of electromagnetic (EM) energy in a load, andspecifically with using EM energy for thawing, heating and/or andcooking.

BACKGROUND OF THE INVENTION

The microwave oven is a ubiquitous feature in modern society. However,its limitations are well known. These include, for example, unevenheating and slow absorption of heat, especially for thawing (ordefrosting). In fact, ordinary microwave ovens, when used for thawingand even heating, result in foods in which the one part may be generallywarm or even partly cooked or overcooked before another part is evendefrosted. Thawing and warming of objects using conventional microwaveovens typically suffers from uneven and typically uncontrolleddissipation of energy in the load.

SUMMARY OF THE INVENTION

The present invention, in some embodiments thereof, stems from theinventors' realization that equal dissipation of energy into a loadduring thawing may result at times in a non-even temperature profile ofthe load, and possibly in thermal runaway phenomena (in which thetemperature in one part of the load increases much faster than in otherparts). In particular, thermal runaway can result in a situation where achange in temperature of a warmer portion beyond a certain point causesan increased rate of change in temperature in that portion therebycontinuously increasing the temperature gap.

In an exemplary embodiment of the invention, energy dissipation iscontrolled in one or more of three manners: (a) reducing maximumdissipated energy (e.g., at all or a portion of the transmittedfrequencies); (b) causing more efficient energy dissipation into theload at frequencies where the dissipation rate is low as compared tofrequencies where dissipation is high; and/or (c) monitoring the loadclosely enough to avoid overheating between monitoring acts. Optionally,less power is differentially dissipated in particular in portions of theload where thermal runaway is a greater danger, for example, in liquidwater portions.

In an exemplary embodiment of the invention, rather than use/measure thedissipation rate, what is measured is a dissipation ratio (e.g., ratiobetween input and dissipation) or even a normalized dissipation ratio,normalized, for example, to a range of 0 to 1 or normalized to anaverage dissipation ratio.

In an exemplary embodiment of the invention, the dissipated power v.dissipation ratio graph is quasi-Gaussian, rather than an essentiallyreverse correlation. At low dissipation ratios it may be desirable todissipate more power but such dissipation is limited by the poordissipation ratio, even if the maximal available power setting is used.At the highest dissipation ratio it may be desirable to transmit nothing(or very little). The intermediate levels are affected by bothtendencies, hence the quasi Gaussian shape.

In an exemplary embodiment of the invention, it is assumed that eachfrequency represents a load portion or portions. A same portion of theload may absorb at multiple frequencies. In an exemplary embodiment ofthe invention, it is assumed that the dissipation at a frequency iscommensurate with the dissipation in those portions.

In an exemplary embodiment of the invention, the maximum applied energy(hpl) is calculated based on spectral information of the load.Optionally or alternatively, the selection of power level per frequencyis selected according to such properties. Optionally or alternatively,selection of power per frequency is based on a selection of a subset offrequencies in which to have more power dissipate into the load.Optionally or alternatively, selection of power per frequency, for eachfrequency, is based on analysis of the spectral information acquired atall frequencies of that band, or based on spectral information acquiredat all frequencies that are considered to be coupled to the load (e.g.,without bands that are with a high Q values, e.g. above 0.25%, or 0.5%or 1%).

In an exemplary embodiment of the invention, the spectral information isanalyzed to distinguish thawed and unthawed portions. Optionally, suchdistinction is based on general properties of the spectral information,rather than on a frequency by frequency analysis, for example, assuminga bimodal distribution of a spectral dissipation image between ice andwater can allow to separate ice and water on a gross basis according tomatching to the expected bimodal distribution. At times, the there is anoverlap between the two modes, wherein a frequency dissipates to someextent in both water and ice portions of the load.

In an exemplary embodiment of the invention, the thawing protocolparameters depend on load size and/or volume, for example, correctingfor a method of estimating thawed water/ice content which may be skewedby larger absolute ice content of a large target and/or if it's initialtemperature is near thawing.

In an exemplary embodiment of the invention, the identification of watercontent/high dissipation frequencies is based on an assumption that icehas a lower dissipation than water. Optionally, a threshold value,relative or absolute, is used to detect such frequencies. Optionally, athreshold is provided for relatively pure ice, above which it is assumedthe material is a mixture of ice and water. Optionally, the system ingeneral is designed so that non-load portions have a very lowdissipation or no energy or very little energy is transmitted infrequencies that are expected to dissipate therein. Optionally, a highthreshold is provided, above which it is assumed the absorbing materialis water and therefore low or no power should be transmitted causing lowor no power dissipation into the load. Optionally, intermediatedissipation ratio frequencies are tracked based on an assumption thatthey reflect mixed water ice portions which may all thaw out and/or inwhich there is an intermediate danger of the water content having arunaway thermal event. Optionally, such intermediate frequencies receiveintermediate power levels.

In an exemplary embodiment of the invention, large ice sections (withlow dissipation in all frequencies) are not over compensated for (e.g.,not assumed to be water and therefore receive low power), by detecting,based on the spectral information, that there is large ice and providingmore energy in those frequencies, until indications of small icesections start appearing in the spectral information. For example,energy transmission in frequencies with intermediate dissipation ratiosis not reduced to the same extent as that of frequencies with highdissipation ratios, in case such frequencies represent large ice.

In an exemplary embodiment of the invention, these and/or otherparameters, such as thresholds, power/frequency ratios and times dependon load properties and/or desired heating effect. Optionally, a tablewith various options is stored in memory and a user can select.Optionally or alternatively, a series of functions are provided andapplied according to user or automatic selection.

Optionally or alternatively, the maximum power level is calculated usingtrial and error methods and/or as a function of average dissipation in aload.

In an exemplary embodiment of the invention, the maximum applied powerlevel and/or frequency dependent power level are updated during thawingor other heating or energy applying process. Optionally, this updatingoccurs a plurality of times (for example, practically continuously, suchas 1000/sec or 2/sec or even once every 5 seconds or more) during thethawing process.

In an exemplary embodiment of the invention, the time between scansand/or dissipation between scans is selected to reduce the danger ofoverheating and/or thermal runaway. Optionally, the power levels used,thresholds, scanning rate and/or other parameters depend on scenarios tobe avoided. In one example, if a small amount of water is mistake for alarge amount of ice (and thus irradiated with high power), the scansettings and/or hpl are selected so that the next scan would detect suchan effect (caused by the amount of water growing in a manner that itwould not be mistaken for ice.

Optionally, the load and/or cavity are manipulated to improve thespectral information, for example, to assist in distinguishing waterfrom ice. This may allow the calculation of a higher power level fortransmission (e.g. average) and/or a higher dissipation ratio (e.g.average or minimal) and thus allow a faster thawing with sufficientquality. For example, the position of the load in the cavity may bechanged (e.g. by rotating or agitating a plate on which the load isplaced) and the spectral information would be compared between aplurality of positions. Optionally, energy transmission will take placewith the load positioned such that the spectral information acquired ismost useful for the ice/water distinction (e.g., having the highestcalculated hpl).

In an exemplary embodiment of the invention, a minimum low power levelis dissipated at frequencies where power was previously applied, toprevent cooling and/or refreezing of such thawed portions. Optionally oralternatively, the maximum power allowed to dissipate into the load at agiven frequency between a first and second acquisition of spectralinformation is such that a thawed portion would not heat up much abovethawing before power is stopped based on change in spectral information.

In an exemplary embodiment of the invention, rather than apply exactamounts of power, use is made of frequent feedback. Optionally oralternatively, the method of applying power takes into accountproperties of the power amplifiers used.

The inventors hypothesize that uneven temperature profiles may be causedor exacerbated by one or more of the possibilities detailed below.However, it should be noted that the methods described herein may alsobe applied independent of such hypothesis. Furthermore, it is noted thatin accordance with some embodiments of the invention, what is avoided isnot uneven temperatures per se, but rather overheating or danger ofoverheating in significant parts of the load (e.g., 0.1%, 0.5%, 1%, 2%,5%, 10% or intermediate percentages, e.g., depending on application,user desires).

(a) Non-uniform composition. A real-life load normally comprisesdifferent materials (e.g. fat, bone, skin and muscle in a chickenportion or air pockets within ground meat or icicles forming betweenshrimp in a shrimp package) which have different specific heat (C_(p))and/or different latent heat (L). In such case, equal dissipated energymay result in unequal temperatures (as RF heating is normally fasterthan heat transfer by conduction within the object). In accordance withsome embodiments of the invention this is taken into account (e.g.,using a preset table) when determining power levels for load portionsassociated with such different materials.

(b) Non-uniform thermal state and heat transfer behavior. The load mayhave different temperatures at different locations (either initially orduring thawing). This may be due for example to non-equilibrated coolingbefore thawing commenced (e.g. the interior being warmer than theexterior, if freezing was incomplete or vice versa, if a frozen objectwas briefly exposed to a higher temperature than its own) or to exposureof the load's surface to different environments, before or duringheating (warm air, internal and external convection currents, coldplate, possibly during heating) or to heterogeneous composition asmentioned above or to an irregular shape of the load (with some portionsbeing thinner than others), or to an irregular shape of the load, e.g.,whereby different portions might have a different surface/volume ratios,or a combination of two or more of the aforesaid. This may result in arelatively warm portion(s) passing through phase change long before thecooler portion(s) will have begun the phase change (even if the load is100% homogeneous and the energy dissipation to all portions thereof isidentical). In an exemplary embodiment of the invention, the heatingprotocol takes such uneven temperatures and/or heat dissipation intoaccount during heating. Optionally, such taking account is automatic bydirecting most power to ice portions.

(c) Temperature-dependent heating. For many types of material the amountof energy required to engender phase change will cause a significantincrease in temperature (e.g. by 20, 40 or even 80° C.) if applied tothe matter after phase change. As a result, equal dissipation of energyin frozen material may result in the warmer portion(s) overheatingbefore phase change will have been completed in the cooler portion(s).In an exemplary embodiment of the invention, such overheating is avoidedby reducing power to areas that are sensitive to overheating and/orwhere power/heat ratio indicates faster heating material.

It is noted that the above may apply at times also to heating of a loadwhere there is no thawing, whether there is phase change (e.g. boiling)or not (e.g. raising the temperature of a load and/or maintaining it ata desired level).

In accordance with an exemplary embodiment of the invention, unevenheating, or at least thermal runaway, are avoided, at least to someextent, if significantly more RF energy is dissipated in sections thatdid not undergo phase change than in sections that have already phasechanged. One particular example is dissipating more power in thawedportions than in non-thawed portions, fat and/or other non-frozenmaterials.

In an exemplary embodiment of the invention, such uneven distribution ofenergy dissipation is achieved by transmitting a high power atfrequencies having a relatively low dissipation ratio or frequenciesthat dissipate primarily in ice, whilst transmitting a low (or even no)power at frequencies that have a relatively high dissipation ratio orfrequencies that dissipate primarily in water.

In accordance with exemplary embodiments of the invention, it is notedthat the dissipation of a given frequency in different load portions(e.g. water and in ice or load portions having different dissipationratios for any other reasons, including, for example, polarity, lipidcontent and water content) depends on many factors, including the loadcomposition, size, shape, location and orientation within the cavity andthe exact temperature and phase in different portions of the load. Underdifferent conditions a given frequency may dissipate mainly in water,mainly in ice or in both. However, the inventors discovered that whenobtaining spectral information from the cavity, an analysis of theobtained information may be used to deduce a useful thawing protocoland/or may reflect the pattern of dissipation in water and/or ice thatmay occur.

In the context of the present application, the term “spectralinformation” means the interaction data for RF in the chamber atdifferent frequencies and/or with the load in the chamber, for example,sweeping the frequency at a constant or changing power using one or morecavity feeds at a time and measuring the reflected power received bysaid one or more cavity feeds, optionally taking into account the poweractually transmitted into the cavity at each frequency. At times onefeed is transmitting while one or more other feeds (or all other feeds)measure the reflected power. At times, the process is repeated for oneor more of the plurality of feeds. A non-limiting example is theobtaining of a spectral image as described in PCT publicationWO07/096,878.

In an exemplary embodiment of the invention, a restraining function isused for calculating the RF power, to transmit into a cavity such that asmaller amount of energy (or no energy at all) dissipates into theportions that have a relatively high dissipation ratio, while a largeramount of energy will dissipate into the portions that have a relativelylow dissipation ratio. In an exemplary embodiment of the invention, thefunction is selected so that energy dissipated per volume unit (or thedissipation per mass unit) is smaller for portions with a highdissipation ratio, as compared to portions with a low or intermediatedissipation ratio. In an exemplary embodiment of the invention, arestraining function is used for calculating the RF power to transmitinto a cavity such that a smaller amount of energy (or no energy at all)will dissipate into the load by frequencies that have a relatively highdissipation ratio, while a larger amount of energy will dissipate intothe load by frequencies that have a relatively low dissipation ratio. Inan exemplary embodiment of the invention, the heating automaticallyand/or inherently adjusts for portions of the load becoming thawed (orpartially thawed) (or frequencies that increase in dissipation ratiointo the load) and thereupon reclassified as “high dissipation portions(or frequencies)” (or “intermediate dissipation portions (orfrequencies)”). For example, by performing a frequency scan or sweepafter a heating session, changes may become apparent in the dissipationratios of at least some of the used frequencies, which changes correlateat least in part with phase changes in respective portions of the load.By recalculating the transmission protocol based on the newly acquiredspectral information, the device can self adjust for the progress ofthawing (and/or changes in the location of the load if it shifts duringoperation).

In an exemplary embodiment of the invention, the transmitted energy ateach frequency is selected such that the amount of energy that willdissipate into the load at a frequency having a high dissipation ratio(e.g. 70% or more or 80% or more) may be 50% or less than the energythat is dissipated into the load at frequencies that have a relativelylow dissipation ratio (e.g. 40% or less or 30% or less). At times thiswould be 20% or less, 5% or less, 0.1%, even 0% of the energy dissipatedin frequencies having a low dissipation ratio.

While the above has focused on thawing, it may be applied to other phasechanges or situations where the relationship between power dissipationand heating rate changes abruptly and/or in situations where it isdesired to avoid thermal runaway (e.g., when trying to uniformly heat anobject containing both low dissipation ratio and high dissipation ratiosections, commensurate with a high and low specific heat, and/or a highand low latent heat, respectively). In addition, multiple (e.g., 3, 4,5, or more) differently heated portions may be provided. At times, theplurality of portions of the working band used for heating do notinclude frequencies (or portions) where no energy is transmitted.Optionally, different frequencies are assigned to such multiple portionsbased on their dissipation ratio. However, it is noted that thawing is apoint of particular interest due to the large amount of energy requiredfor the phase change as compared to the energy required for temperaturechange and considering that food is often stored frozen and served orprepared thawed. Similarly, portions which might be damaged byoverheating and/or portions which are unacceptable if not heated enough,may be additionally or alternatively of interest. At times, there mightbe a desire to heat different portions differently for any other reason(e.g. to heat (e.g. cook) one portion but not another or to reachdifferent final temperatures).

It is also noted that while the underlying strategy in some embodimentsis to tailor the power per volume unit according to the effect of suchpower on the targeted load portion, in accordance with some embodimentsthis is achieved in directly by targeting specific frequencies andtailoring power according to the dissipation in those frequencies,without directly ensuring a certain power level per unit volume.

There is provided in accordance with an exemplary embodiment of theinvention, a method of heating a load in using RF, comprising:

(a) providing a load having an overheating temperature point;

(b) selecting a maximum power to be dissipated in the load in a mannerwhich avoids overheating; and

(c) applying RF power to said load at a plurality of differentfrequencies, said power being different at different frequencies andbelow said maximum power at all frequencies.

In an exemplary embodiment of the invention, said selecting comprisestrading off uniformity of heating with speed of heating. At times, themaximum power selected might be the maximum power available by thedevice at any given frequency multiplied by the dissipation ratio atthat frequency. Optionally or alternatively, applying RF power comprisescausing a phase change in said load. Optionally, said phase changecomprises thawing. Alternatively said phase change comprisesevaporation.

In an exemplary embodiment of the invention, said phase change comprisesa ratio of at least 1:20 between the effectiveness of power to causephase change in a load portion unit and the effectiveness of the powerto increase the temperature of a load portion unit that hasphase-changed by 1 degree Celsius.

In an exemplary embodiment of the invention, said power is selected andapplied in a manner which avoids thermal runaway in said load duringsaid applying.

In an exemplary embodiment of the invention, selecting a maximum powercomprises selecting a maximum power as a function of an averagedissipation of the load.

In an exemplary embodiment of the invention, selecting a maximum powercomprises selecting a maximum power as a function of spectralinformation of the load.

In an exemplary embodiment of the invention, the method comprisesselecting a minimum power to apply at frequencies where power isapplied.

In an exemplary embodiment of the invention, the method comprisesselecting a power for each of said plurality of frequencies. Optionally,selecting a power comprises selecting one or more sub-bands offrequencies to power, within a wider bandwidth of a system used forapplying said RF power.

In an exemplary embodiment of the invention, the method comprisesrepetitively retrieving spectral information of said load and using saidinformation to guide at least one of said selecting and said applying.

In an exemplary embodiment of the invention, applying said RF powercomprises applying power at a frequency with an inverse ratio to adissipation ratio at said frequency.

In an exemplary embodiment of the invention, the method comprisesavoiding applying power at frequencies with a dissipation ratio below alow threshold level.

In an exemplary embodiment of the invention, the method comprisesavoiding applying power at frequencies with a dissipation ratio above ahigh threshold level.

In an exemplary embodiment of the invention, said applying is responsiveto identifying ice in said load and wherein said identifying comprisesidentifying according to frequencies with low dissipation. Optionally,identifying is compensated for the mass of the load. Optionally oralternatively, identifying is according to a threshold which isdependent on the load type.

There is provided in accordance with an exemplary embodiment of theinvention, apparatus configured to carryout the selecting and applyingof any of the preceding claims.

There is provided in accordance with an exemplary embodiment of theinvention, a method of heating a load using RF, comprising:

(a) providing a load having a different dissipation ratios at differentportions;

(b) setting frequency/energy pairs such that in heating the load lessenergy (or power) is transmitted at frequencies that dissipate at afirst dissipation ratio than at frequencies that dissipate at a seconddissipation ratio, wherein said second dissipation ratio is higher thansaid first dissipation ratio in a given transmission cycle; and

(c) applying said frequency power pairs to heat said load.

There is provided in accordance with an exemplary embodiment of theinvention, a method of heating a load using RF, comprising:

(a) providing a load having a different rate of heating per transmittedenergy (h/te) applied at different portions;

(b) setting frequency/energy pairs such that in heating the load lessenergy per unit volume of portions is transmitted at frequencies thatcorrespond to portions with a high h/te rate than at frequenciescorresponding to portions with a low h/te; and

(c) applying said frequency power pairs to heat said load.

There is provided in accordance with an exemplary embodiment of theinvention, a method of heating a load using RF, comprising:

(a) providing a load having different dissipation ratios at differentportions;

(b) setting frequency/power pairs such that in heating the load adifferent power application protocol is applied at frequencies thatdissipate at a first dissipation ratio and at frequencies that dissipateat a second dissipation ratio; and

(c) applying said frequency/power pairs to heat said load.

In an exemplary embodiment of the invention, said applying comprisesapplying more power for a portion with a lower dissipation ratio.Optionally or alternatively, a difference between two or more powerapplication protocols comprises a total amount of energy per load amountto be dissipated in their respective load portions. Optionally oralternatively, a difference between two or more power applicationprotocols comprises a tradeoff between heating velocity and homogeneity.

In an exemplary embodiment of the invention, said setting comprisesassociating frequencies into sets associated with dissipation ratios;and wherein said setting comprises selecting frequency/power pairsaccording to said sets. Optionally, said setting comprises selecting apower level per set. Optionally or alternatively, said associatingcomprises associating based on information in addition to saiddissipation ratio. Optionally or alternatively, at least one setincludes a plurality of non-continuous frequency ranges with at leastone frequency belonging to another set between said ranges. Optionallyor alternatively, at least one set corresponds to frozen material.Optionally or alternatively, associating comprises associating into atleast three sets. Optionally or alternatively, said associatingfrequencies into sets is performed by associating into a preset numberof sets. Optionally, said preset number of sets is between 2 and 10sets.

In an exemplary embodiment of the invention, associating comprisesassociating into at least two sets each having a significant amount ofdissipated energy or power assigned to a plurality of frequenciestherein, said significant amount being at least 7% of a total dissipatedpower in a heating cycle being assigned to a set. Optionally oralternatively, at least two of said sets have a non-zero transmittedpower and wherein an average dissipated power of one set is at leasttwice that of another set. Optionally or alternatively, at least two ofsaid sets have a non-zero transmitted power and wherein an averagedissipated power of one set is at least five times that of another set.Optionally or alternatively, at least two of said sets have a non-zerotransmitted power and wherein an average dissipated power of one set isat least ten times that of another set. Optionally or alternatively, aset or sets for which power is transmitted cover at least 5% of workingfrequencies. Optionally or alternatively, a set or sets for which poweris transmitted cover at least 20% of working frequencies. Optionally oralternatively, at least two of said sets each correspond to adissipation ratio range of values of at least 10%.

In an exemplary embodiment of the invention, said load comprises food.Optionally or alternatively, said load comprises a combination of atleast two food portions. Optionally or alternatively, said applyingcauses a phase change in said load. Optionally or alternatively, saidapplying causes a thawing of at least a part of said load.

In an exemplary embodiment of the invention, the method comprisesrepeating (b) and (c) at least twice as part of a heating process.

There is also provided in accordance with an exemplary embodiment of theinvention, a method of heating a load using RF, comprising:

(a) providing a load having a different rate of heating per powerapplied (h/p) at different portions;

(b) setting frequency/power pairs such that in heating the load lesspower per unit volume of portions is transmitted at frequencies thatcorrespond to portions with a high h/p rate than at frequenciescorresponding to portions with a low h/p; and

(c) applying said frequency power pairs to heat said load.

There is also provided in accordance with an exemplary embodiment of theinvention, apparatus configured to carryout the selecting and applyingof any of the preceding claims. Optionally, the apparatus comprises amemory having a plurality of power application protocols stored thereinand configured to apply different protocols to different sets offrequencies.

There is also provided in accordance with an exemplary embodiment of theinvention, a method of heating a load in using RF, comprising:

(a) providing a load having an overheating temperature point;

(b) selecting a maximum power to be dissipated in the load in a mannerwhich avoids overheating; and

(c) applying RF power to said load at a plurality of differentfrequencies, said power being different at different frequencies andbelow said maximum power at all frequencies. Optionally, applying RFpower comprises causing a phase change in said load. Optionally, saidphase change comprises thawing. Optionally or alternatively, said phasechange comprises evaporation.

In an exemplary embodiment of the invention, said phase change comprisesa ratio of at least 1:20 between the effectiveness of power to causephase change in a load portion unit and the effectiveness of the powerto increase the temperature of a load portion unit that hasphase-changed by 1 degree Celsius.

In an exemplary embodiment of the invention, said power is selected andapplied in a manner which avoids thermal runaway in said load duringsaid applying. Optionally or alternatively, selecting a maximum powercomprises selecting a maximum power as a function of an averagedissipation of the load. Optionally or alternatively, selecting amaximum power comprises selecting a maximum power as a function ofspectral information of the load. Optionally or alternatively, selectinga maximum power comprises selecting a maximum power as a function of themaximal power that may be transmitted by the device into the cavity atany given frequency.

In an exemplary embodiment of the invention, the method comprisesselecting a minimum power to apply at frequencies where power isapplied. Optionally or alternatively, the method comprises selecting apower for each of said plurality of frequencies. Optionally, selecting apower comprises selecting one or more sub-bands of frequencies to power,within a wider bandwidth of a system used for applying said RF power.

In an exemplary embodiment of the invention, the method comprisesretrieving spectral information of said load and using said informationto guide at least one of said selecting and said applying. Optionally,said retrieving of spectral information is performed repetitively.

In an exemplary embodiment of the invention, applying said RF powercomprises applying power at a frequency with an inverse relation to adissipation at said frequency.

In an exemplary embodiment of the invention, the method comprisesavoiding applying power at frequencies with a dissipation ratio below alow threshold level.

In an exemplary embodiment of the invention, the method comprisesavoiding applying power at frequencies with a dissipation ratio above ahigh threshold level.

In an exemplary embodiment of the invention, said applying is responsiveto identifying ice in said load and wherein said identifying comprisesidentifying according to frequencies with low dissipation. Optionally,identifying is compensated for the mass of the load. Optionally oralternatively, identifying is according to a threshold which isdependent on the load type.

In an exemplary embodiment of the invention, said applying comprisesnormalization of dissipation ratio values.

In an exemplary embodiment of the invention, applying power comprisesapplying different aggregate amounts of power, for a given time period,such that an actual power for a certain frequency is fixed, but aduration of application of the power within a time period is variedbetween frequencies, yielding a different effective aggregate power fordifferent frequencies.

In an exemplary embodiment of the invention, applying power comprisesgrouping a plurality of said frequencies into a plurality of sets andvarying the amount of power applied on the basis of applied power perset.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary non-limiting embodiments of the invention are described belowwith reference to the attached figures. The drawings are illustrativeand generally not to an exact scale. The same or similar elements ondifferent figures are referenced using the same reference numbers.

FIG. 1 schematically depicts a device in accordance with an exemplaryembodiment of the present invention;

FIG. 2 is a simplified flow chart of a method of operation of a thawingdevice in accordance with an embodiment of the invention;

FIG. 3 is a graph of relative compensation vs. normalized dissipationratio for an exemplary decision function;

FIG. 4 is a is a simplified flow chart of a method of operation of adevice in accordance with another embodiment of the invention;

FIG. 5 is a chart illustrating a method of selecting an hpl parametervalue as a function of average dissipation;

FIG. 6 is a chart showing measured dissipation ratios, in average and atvarious frequencies for bovine flesh and tuna fish flesh having the samemass;

FIG. 7 is a chart showing measured dissipation ratios, in average and atvarious frequencies for a large chicken and for a small chicken;

FIG. 8 is a flowchart of a method of differentially heating materialswith different dissipation ratios, in accordance with an exemplaryembodiment of the invention;

FIG. 9 shows an exemplary alternative to the example of FIG. 3; and

FIG. 10 shows different dissipation ratios for a mixture of rice andchicken.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Overview

The present application describes, inter alia, a number of advances inthe field of RF heating (e.g. microwave or UHF) heating. While, forconvenience these advances are described together in the context ofvarious apparatus and methods, each of the advances is generallyindependent and can be practiced with prior art apparatus or method (asapplicable) or with a non-optimal version of the other advancesdescribed herein. Furthermore, advances described in the context of oneembodiment of the invention can be utilized in other embodiments andshould be considered as being incorporated as optional features in thedescriptions of other embodiments, to the extent possible. Theembodiments are presented in somewhat simplified form to emphasizecertain inventive elements. Furthermore, it is noted that some featuresthat are common to some or all embodiments of the invention may bedescribed in the section entitled “Summary of the Invention” and shouldalso be considered as being part of the detailed description of thevarious embodiments.

A method and device for providing essentially equal dissipation ofenergy in a general irregular load follows PCT publication WO07/096,878to Ben-Shmuel and Bilchinsky ('878) incorporated herein by reference. Inan exemplary embodiment, a device according to '878 uses informationthat is obtained by transmitting a plurality of RF frequencies (allwithin a band of frequencies) into a cavity to obtain the fullS-parameters of the cavity within that band, thereby being able todetermine the spectral information of the cavity (e.g., dissipation ofenergy into the cavity) as a function of frequency. This information isused to deduce at which power (if any) each of the swept frequenciesshould be transmitted into the device in order to obtain a desireddissipation pattern within the cavity.

In one option, the power is transmitted only in bands that primarilydissipate in the load (and not surface currents or between antennas).This can be performed for example such that the product of theefficiency 11 and the power fed is substantially constant for alltransmitted frequencies, and it allows an essentially equal dissipation(as a function of frequency) of energy in the load or the cavity,regardless of the load's composition.

During thawing of an object, ice in the object melts to water. Ice andwater have different absorption for RF energy, resulting in a differentreturn loss and coupling as a function of frequency. This may changematching, and after re-matching by adjustment of the matching elements,the frequency of the absorption efficiency peak may change. Optionally,by monitoring the frequency that is chosen for input (based on theacquired information) and especially its rate of change, the point atwhich all of the ice has melted to water can be determined and heatingterminated (if only thawing is desired).

Exemplary System

FIG. 1 schematically depicts a device 10 according to an embodiment ofthe present invention. In an exemplary embodiment of the invention, thedevice is constructed and operated as described in WO07/096,878, withone or more of the changes detailed below. In particular, in anexemplary embodiment of the invention, the controller is configured suchthat power transmission is avoided to high absorption portions (forexample corresponding to thawed portions or more polar portions orportions having a lower fat or higher water or salt content) so thatdanger of overheating is reduced. Additionally or alternatively, a, forexample, significantly lower power is provided to defrosted portions, aspower needed for temperature change and thawing in unthawed areas ismuch higher than needed for heating of fluid parts, so providing asimilar power level would cause runaway heating of thawed portions andonly mild heading/thawing of unthawed portions.

Device 10, as shown, comprises a cavity 11. Cavity 11 as shown is acylindrical cavity made of a conductor, for example a metal such asaluminum. However, it should be understood that the general methodologyof the invention is not limited to any particular resonator cavityshape. Cavity 11, or any other cavity made of a conductor, operates as aresonator for electromagnetic waves having frequencies that are above acutoff frequency (e.g. 500 MHz) which may depend, among other things, onthe geometry of the cavity. For example—a broad band of RF frequenciesmay be used, for example 800-1000 MHz. Methods of determining a cutofffrequency based on geometry are well known in the art, and may be used.

A load 12 is placed within the cavity, optionally on a supporting member13 (e.g. a conventional microwave oven plate). In an exemplaryembodiment of the invention, cavity 11 comprises one or more feeds 14(e.g. antennas) which may be used for transmitting RF energy into thecavity. The energy is transmitted using any method and means known inthat art, including, for example, use of a solid state amplifier. One ormore, and at times all, of the feeds 14 can also be used one or moretimes during the heating process for obtaining the spectral informationof the cavity within a given band of RF frequencies to determine thespectral information of the cavity (e.g., dissipation of energy into thecavity) as a function of frequency in the working band. This informationis collected and processed by controller 17, as will be detailed below.

In an exemplary embodiment of the invention, cavity 11 also comprisesone or more sensors 15. These sensors may provide additional informationto controller 17, including, for example, temperature (e.g., by one ormore IR sensors, optic fibers or electrical sensors), humidity, weight,etc. Another option is use of one or more internal sensors embedded inor attached to the load (e.g. an optic fiber or a TTT as disclosed inWO07/096,878).

Alternatively or additionally, cavity 11 may comprise one or more fieldadjusting elements (FAE) 16. An FAE is any element within the cavitythat may affect its spectral information or the spectral informationderivable there from. Accordingly, an FAE 16 may be for example, anyobject within cavity 11, including one or more of metal componentswithin the cavity, feed 14, supporting member 13 and even load 12. Theposition, orientation, shape and/or temperature of FAE 16 are optionallycontrolled by controller 17. In some embodiments of the invention,controller 17 is configured to perform several consecutive sweeps. Eachsweep is performed with a different FAE property (e.g., changing theposition or orientation of one or more FAE) such that a differentspectral information may be deduced. Controller 17 may then select theFAE property based on the obtained spectral information. Such sweeps maybe performed before transmitting RF energy into the cavity, and thesweep may be performed several times during the operation of device 10in order to adjust the transmitted powers and frequencies (and at timesalso the FAE property) to changes that occur in the cavity duringoperation.

In an exemplary embodiment of the invention, the FAEs are controlledand/or load rotated or moved, so that a most useful spectral informationis acquired for selective irradiation and/or for setting of radiationparameters such as hpl, for example as described below. Optionally oralternatively, the load and/or FAEs are periodically manipulated and/orbased on a quality or other property of acquired spectral information.Optionally, the setting are selected which allow a highest hpl to beselected.

An exemplary transfer of information to the controller is depicted bydotted lines. Plain lines depict the control exerted by controller 17(e.g., the power and frequencies to be transmitted by an feed 14 and/ordictating the property of FAE 16). The information/control may betransmitted by any means known in the art, including wired and wirelesscommunication.

Exemplary Thawing

Attention is drawn to FIG. 2, which depicts a flowchart 20 showing howthe device 10 may be operated to thaw a frozen load (e.g. food)according to an exemplary embodiment of the invention.

After load 12 is placed in cavity 11, a sweep 21 is performed. Sweep 21may comprise one or more sweeps, allowing the obtaining of an average ofseveral sweeps, thereby obtaining a more exact result. Additionally oralternatively, sweep 21 may be repeated with different FAE properties ordifferent load/plate positions (optionally the sweep is performedseveral times at each configuration) and/or using different antennas fortransmitting/sensing.

In order to improve the accuracy of the analysis of the sweep results,in an exemplary embodiment, the amount of power that is actuallytransmitted (e.g. if the power transmitted at different frequencies isnot identical) at each frequency is included in the calculation, inorder to deduce the percent of transmitted energy that is dissipated inthe cavity. Such differences in power transmission between frequenciesmay, for example, be an inherent feature of the device and/or a devicecomponent, such as the amplifier.

Once one or more sweep results are obtained, an analysis 22 isperformed. In analysis 22 a thawing algorithm is used to define thetransmission frequencies and the amount of energy to be transmitted ateach frequency based on the spectral information that was obtained atsweep 21 (optionally in conjunction with other input methods, such as amachine readable tag, sensor readings and/or the user interface).Consequently, energy 23 is transmitted into the cavity, optionally asdictated by analysis 22. Optionally, the desired dissipated power isbelow the expected power which is below the maximum power multiplied bythe dissipation ratio.

In an exemplary embodiment of the invention, the load is scanned 120times in a minute. Higher (e.g. 200/min, 300/min) or lower (e.g.,100/min, 20/min, 2/min, 10/thawing time, 3/thawing time) rates may beused, as well as uneven sampling rates. At times, a scan sequence (e.g.,one or more scans) may be performed once every 0.5 seconds or once every5 seconds or at any other rate, such as higher, lower or intermediate.Moreover, the period between scans may be defined by the amount ofenergy to be transmitted into the cavity and/or the amount of energy tobe dissipated into the load. For example, after a given amount of energy(e.g. 10 kJ or less or 1 kJ or less or several hundreds of joules oreven 100 J or less were transmitted or dissipated into the load or intoa given portion of a load (e.g. by weight such as 100 g or bypercentage, such as 50% of load)), a new scan is performed. In somecases, the information is provided using other means, such as anRF/bar-code readable tag (e.g., with previous scanning information orthawing presets) or using temperature sensors.

In an exemplary embodiment of the invention, the rate of sweepingdepends on the rate of change in spectral information between sweeps,for example, a threshold of change in dissipation and/or frequencies(e.g., a 10% change in sum integral) may be provided or different changerates associated with different sweep rates, for example using a table.In another example, what is determined is the rate of change betweensweeps (e.g., if the average change between sweeps was less than thechange between the last two sweeps). Such changes may be used to adjustthe period between scans once or more than once during heating.Optionally or alternatively, changes in the system (e.g. movement of theplate) may affect the sweep rate (typically major changes increase therate and minor or no changes decrease it).

This process is optionally repeated for a predetermined period of timeor until termination by a user. Alternatively, the thawing process maybe terminated automatically 24. At 24, which may be performed after eachsweep, before each energy transmission and/or at any other stage of theprocess, sweep results and/or a sensor reading are used to decidewhether or not thawing may be or should be stopped. For example—if aphase change completion is detected or if the object's temperature ismeasured to be above a given temperature (e.g. outer temperature 5° C.or more), thawing may be terminated. In another example, if the totalenergy dissipated into the load reaches a predetermined amount of energythat is needed for thawing to a desired final temperature (e.g. takinginto account the load's initial temperature and composition). Thawingmay be stopped. A modification of the flowchart may be used for anyother heating process, including for example heating (with or withouttemperature elevation) and drying. In such cases, the termination pointmay be defined also by other parameters, including a measuredtemperature, a desired total amount of dissipated energy in the load,the level of humidity, rate of temperature change, etc.

The (frequency/energy) or (frequency/power) pairs for thawing areoptionally selected to increase (or even maximize) energy dissipation infrequencies that have low dissipation ratios in the load (e.g.predominantly solid or ice portions) and reduce (or even minimize)energy dissipation at frequencies that have a relatively highdissipation ratio (e.g. predominantly thawed portion, such as liquid orwater). For example, in low dissipation ratios, the device will be setto produce efficient power dissipation (e.g., as a factor of thepossible maximal dissipation possible) while at the high dissipationratios, the device will be set to dissipate much less energy than may bedissipated. At times, such as when the time for transmitting eachfrequency is fixed, the (frequency/energy) pairs may be(frequency/actual power) pairs. As used herein, power is not necessarilya direct function of time, but may be an indirect function of time. Forexample, if, within a given time period, such as a minute a fixed poweris used, but the duration of application of power is changed (e.g., from1 to 2 seconds), then the net result is a difference in energy appliedper the certain time unit, which is power. Thus, frequency/power pairscan include frequency/energy pairs with an application protocol. Itshould also be noted that one a protocol is decided for a set of drvalues, this may be implemented by providing frequency/power settings,which can vary over time for a same frequency, over time. Further, asdescribed below, a frequency/power pair may be associated directly witha set of frequencies, with the actual assignment of power to a frequencydecided as part of the application protocol.

An exemplary thawing algorithm transmits zero power (or energy) atfrequencies with dissipation ratio above a predetermined threshold (e.g.70% dissipation or 70% normalized dissipation, as explained below)) ofthe maximum dissipation ratio in the selected working frequency range[f₁, f₂] and non-zero powers at other frequencies of that range. In somecases, the powers are selected in a binary fashion—either maximal orminimal. In some cases, the different amounts of power (relative toother frequencies, or absolute) are transmitted by allowing a differenttransmission time for different frequencies in a cycle. Alternatively,intermediate, power levels (or energy amounts) are provided, for examplefor portions with intermediate dissipation levels.

In an exemplary embodiment of the invention, when power is provided to afrequency or frequency set this power level is selected to besignificant. For example, such significance can be measured as afunction of the total power provide din a scanning/transmission cycle(e.g., 5%, 10%, 20% or smaller or larger or intermediate values).Optionally or alternatively, this significance can be measured as aneffect on temperature of a portion of at least 5% of the load in acycle, for example, being at least 0.1° C., 0.2° C., 0.5° C. or smalleror intermediate or higher temperature changes. Optionally oralternatively, significance can be measured based on the a mount ofphase changed caused by the power dissipated, for example, being enoughto change a spectral image (RMSE) by at least 1%, 3%, 5%, 10% or smalleror intermediate or larger amounts in a cycle or over a period of timesuch as 30 seconds.

In an exemplary embodiment of the invention, the device includes amemory having stored thereon a plurality of threshold values, hplvalues, dissipation/power ratios, dissipation/energy ratios and/orparameters for various load properties. Optionally, the device and/orthe user select between such stored options as an initial setting or asa final setting for thawing. For example, a fixed hpl of 80% (of themaximal power of the amplifier at each frequency) may be used for frozenbovine meat of a certain weight.

Exemplary Thawing Algorithm

An exemplary thawing algorithm is the following. In a selected workingrange [f₁, f₂], high and low boundary powers (hpl, lpl) are selected andany applied power is maintained between these boundaries.

The boundary low power level (lpl) is the minimum power level wheredissipation in the load is high enough to be useful. For example, if 15%is selected to be the minimal useful dissipation, lpl will be set foreach frequency to be 15% of the maximal power that may be transmitted.Alternatively it may be set at a pre-selected low power for allfrequencies (e.g., 60 Watts or less) or any combination of theaforementioned; if the dissipation in the load at a given frequency isbelow lpl, the transmitted power at that frequency will be set at zero.

The boundary high power level (hpl), determines the highest alloweddissipated power. This means that the highest power outputted isconstrained to avoid undesired thermal effects. In addition, the actualpower outputted at a given frequency may be selected according tospectral information, in particular, to selectively target unthawedareas. Optionally, the power levels are generally inversely related todissipation. As may be noted, reducing maximum oven power will generallylengthen thawing times. In some cases, the power levels applied meet abinary criterion: hpl for low dissipating portions and some other value(such as zero) for high dissipating areas.

Using an excessively high hpl may cause an unacceptable uneventemperature distribution in the load and may result in thermal runaways.The more sensitive a load is to transmitted power (e.g., at a certainworking band), the lower would be the power of an acceptable hpl.Optionally, the working band is selected according to which working bandbetter distinguishes water from ice.

Generally, for sensitive loads, a low hpl is set, but such hpl may beused also for less sensitive loads, albeit at the cost of increasing thethawing time. Nonetheless, at times it may be preferred to set for eachload the highest hpl that would provide an acceptable post thawtemperature distribution in the load (e.g. ±15° C., ±10° C., ±5° C., ±2°C. or even more uniform). The acceptable post thaw temperaturedistribution can depend, for example, on one or more of the compositionof the load, its sensitivity to overheating (e.g. whether damage iscaused; its extent and reversibility; and to what extent the damage ismaterial) and the purpose for which the load is intended. It is notedthat at times, speed of thawing is preferred over quality, in which casea higher hpl may be used, and the post thaw quality would be suboptimal.Optionally, the device is provided with a user selectable tradeoff(e.g., knob or data input) between uniformity, maximum temperatureand/or rate of thawing.

It is noted that in accordance with some embodiments of the invention,prevention of hot spots is actively preferred over uniformity ofthawing, heating and/or energy dissipation.

Optionally, hpl is set low enough so that a thawed section will not beover heated before heating at its respective frequencies is stopped orreduced.

Exemplary Methods of Determining hpl (High Power Level)

hpl may be determined in various manners, for example, by trial anderror. In an exemplary embodiment of the invention, several hpl settingsare tried to determine the maximal hpl which would provide an acceptabletemperature distribution in the load, post thawing. Such trials maycontinue during thawing, for example, being performed every scan, everysecond or every minute or at intermediate time scales. In an exemplaryembodiment of the invention, hpl is started at low values and increasedgradually. Optionally, the hpl is set per item type.

In an exemplary embodiment of the invention, preset hpl values areprovided for various combinations of load properties, such as ore or twoor more of shape, weight, temperature, desired effect and/or materialtype. Optionally, a user can select such properties and the device willsuggest and/or use an hpl accordingly.

Optionally, hpl is updated periodically during thawing.

In an exemplary embodiment of the invention, hpl is estimated (initiallyor in an ongoing manner) with the assistance of changing the load and/orcavity so that more useful spectral information is acquired. In general,if the acquired spectral information is better, a better cut-off betweenice and water may be identified, allowing a higher hpl to be used forthe ice sections and allowing a faster heating at a same quality (e.g.,evenness) and/or a higher quality heating at same speed.

Alternatively, and while not wishing to be bound by theory, it isproposed that the sensitivity of the load may be determined based on therelative dissipation of energy in thawed and frozen portions of theload. When the dissipation in frozen portion and thawed portion isrelatively similar (e.g. 10-15% dissipation difference, such as between40% and 50% dissipation ratio) (e.g. due to low water content), thesample is deemed to be of high sensitivity (e.g., the distinctionbetween ice and water requires a more sensitive determination). Thegreater the disparity is between dissipations in thawed and frozenparts, the lower the sensitivity of the load. Therefore, hpl may bedetermined by obtaining the spectral information of the load andcomparing the maximal dissipation (d_(max)) with the minimal dissipation(d_(min)) in a working frequency band. The greater the difference isbetween d_(min) and d_(max) the lesser the sensitivity of the load, andhigher the hpl that should optionally be used.

It is noted that the hpl may be allowed to be higher if a betterselection of power to intermediate dissipation frequencies is provided.

Also alternatively, and while not wishing to be bound by theory, it isproposed that hpl may be determined based on the maximum power that canbe dissipated in the load at each frequency (ep(f)) and ldl. hpl may beset to be such that the portion of the frequencies being used, forexample all frequencies within a working band (e.g. the band spanning800-1000 MHz)) (or other set of frequencies) that are considered todissipate into the load and for which lpl<ep(f)<hpl would be less than apreset threshold. For example, this threshold may be selected to be 10%or 20% or 30% or any value in-between. Optionally, this method is basedon a realization (and/or for cases that) that the device is typicallylimited in maximum power and that practically, the closer the hpl is tothe maximum power, the less easy it may be to provide different powerlevels at different, near, frequencies. Optionally, the percentagedepends on a desired tradeoff between quality and/or speed.

Accordingly, a thawing protocol may use a single hpl value (e.g. ifdedicated to loads having similar sensitivity; or a low hpl that wouldbe suitable for most contemplated loads). Alternatively, the protocolmay use a selection between several possible hpl values (e.g. aselection between a number of preset values or optionally setting thevalue manually or automatically to correspond to a given load and/oracceptable post thaw temperature distribution). Finally, the protocolmay use any value (e.g. calculated automatically or selected manually)within the power capabilities of the device. An example of a relativelyhigh hpl may be 300 Watt or 80% of the maximal power from the amplifierat that frequency. An example of a relatively low hpl may be 120 Wattsor 30% of the maximal power from the amplifier at that frequency.Interim values are possible as well.

Exemplary Determination of Dissipation Function dr(f)

dr(f) denotes the dissipation ratio as a function of frequency, namelythe percentage of transmitted power through each feed (e.g. feed j) thatis dissipated in the load. This function has potential values between 0and 1, and is optionally computed as shown in Equation 1, based on themeasured power and using measured spectral information. However, asnoted herein, a binary function or non-linear and/or non-monotonicfunction may be used (e.g., and determined in a factory or duringcalibration).

$\begin{matrix}\begin{matrix}{{{dr}_{j}(f)} = \frac{{P_{{incident},{watt}}^{j}(f)} - {\sum\limits_{i}{P_{{returned},{watt}}^{i}(f)}}}{P_{{incident},{watt}}^{j}(f)}} \\{= {1 - \frac{\sum\limits_{i}{P_{{returned},{watt}}^{i}(f)}}{P_{{incident},{watt}}^{j}(f)}}}\end{matrix} & \left( {{eq}.\mspace{14mu} 1} \right)\end{matrix}$

Normalization of dr(f)

The dissipation ratio in frozen portions (e.g. ice) is relatively lowerthan that of the thawed portions (e.g. liquid/water), but a large amountof ice can show considerable dissipation. In order to distinguishdissipation in at frequencies having a low dissipation ratio (e.g. ice)from dissipation at frequencies having a high dissipation ratio (e.g.liquid water), while reducing the effect of relative mass, the dr(f)function is optionally normalized to the whole range between 0 and 1;This normalization may be useful also in other cases where thedifference between dissipation in frozen portions and thawed portions isrelatively small, regardless of the cause (e.g., low water content). Thenormalized function—dr′(f)—may be used to calculate the compensationfactors, as shown below.

drh=min {dr(f)}_(f∈[f) ₁ _(,f) ₂ _(])

drl=max {dr(f)}_(f∈[f) ₁ _(,f) ₂ _(])

dr′(f)=(dr(f)−drl)/(drh−drl)  (eq. 2)

In case of some loads the use of dr′(f) is optionally avoided, and inoriginal dr(f) used instead. Optionally, a device is configured to haveboth protocols for alternative use.

The choice between the protocols may be based on user input (e.g. userinterface or machine readable tags) or on a sensor reading within thedevice (e.g. a weight sensor). Alternatively, dr′(f) may be used for allloads.

The maximum power that can be dissipated in the load at each frequency(depicted as ep(f)) is optionally calculated as follows, given thatP_(maximum j, watt) is a maximum power available from the amplifier ateach frequency.

ep _(j)(f)=dr _(j)(f)P _(maximum,j,watt)(f)  (eq. 3)

Using the above, the compensation function (coeff(f)) is optionallycalculated. This function is optionally used to determine the relativeamount of energy that should dissipate in the load at each frequency, asa function of dr′(f) for example as shown in eq. 4A:

$\begin{matrix}{{{coeff}(f)} = {F\left( {{dr}^{\prime}(f)} \right)}} & \left( {{eq}.\mspace{14mu} 4} \right) \\{{F\left( {{dr}(f)}^{\prime} \right)} = \left\{ \begin{matrix}{{dr}^{\prime} < 3} & 0 \\{{dr}^{\prime} > 0.8} & 1 \\{Else} & {{{- 2}\; {dr}^{\prime}} + 1.6}\end{matrix} \right.} & \left( {{{eq}.\mspace{14mu} 4}A} \right)\end{matrix}$

In an exemplary embodiment of the invention, frequencies may beclassified as “ice”, “water” and/or “mixed ice/water” according to theirdissipation ratio. Optionally, higher power is provided into ice andmixed ice/water and plain water is provided with low or no power.

Optionally, there is provided a dissipation threshold below which thedissipation into the load is so low that no power is transmitted, as theload portion is assumed to not be ice. In an exemplary embodiment of theinvention, the device is designed to have a very low intrinsicdissipation at any frequencies or a known dissipation at only somefrequencies (where the threshold may then be raised).

It is noted that large pieces of ice may have a relatively highdissipation. Optionally, if there are no (or few, e.g., below athreshold) low-dissipation frequencies and it is known that the load isfrozen, then it is assumed that the lowest dissipation frequencies areice and power (at regular or somewhat reduced levels) is provided atsuch frequencies, until lower dissipation frequencies appear, indicatingthe formation of smaller frozen regions.

Example dr(f)

An example for a function according to Equation (4) is depicted in FIG.3. As can be seen, two limits are set. At frequencies that dissipateinto the load less than a pre-set threshold (e.g. dr′(f)<0.3 in theexample of FIG. 3) the maximal allowed power which is a minimum betweenthe ep(f)/dr(f) and hpl(f)/dr(f) will be transmitted. At frequenciesthat will at dissipate into the load more than a pre-set value (e.g.dr′(f)>0.8 in the example of FIG. 3) no energy will be transmitted. Atall other frequencies (0.3<dr′(f)>0.8 in the example of FIG. 3) thepower transmission will be calculated using the selected function. Inthe case of FIG. 3 this was a generally linear function, but otherfunctions, optionally non-linear, may be used that provide an inversecorrelation between dr′(f) and coeff(f) (e.g. exponential, stepfunction, piecewise linear, polynomial and/or general look-up table,optionally with interpolation). Optionally, the function prefersapplying power to low-dissipation areas to an extent greater than asimple inverse function. Optionally, the function is selected based on aperceived risk of damage to the load.

Exemplary Actual Power Calculation

gl(f) is the power to be dissipated in the object to be heated, takinginto consideration the maximum power that can be dissipated in the loadat each frequency (ep(f)) and hpl(f) and the compensation function(coeff(f)), as follows:

$\begin{matrix}{{{gl}(f)} = \left\{ \begin{matrix}{{hpl} < {{ep}(f)}} & {{hpl} \cdot {{coeff}(f)}} \\{{lpl} < {{ep}(f)} < {hpl}} & {{{ep}(f)} \cdot {{coeff}(f)}} \\{else} & 0\end{matrix} \right.} & \left( {{eq}.\mspace{14mu} 5} \right)\end{matrix}$

Using gl(f) the power to be transmitted from the amplifier (nopw(f) inorder to cause the desired dissipation in the load, at each frequency,is optionally calculated as follows:

nopw(f)=gl(f)/dr(f)  (eq. 6)

nopw(f) will always be lower than P_(maximum,j,watt(f)), which is themaximum power extractable from an amplifier at each frequency for thefollowing reason:

$\begin{matrix}{\mspace{79mu} {{{gl}(f)} = \left\{ {{\begin{matrix}{{hpl} < {{ep}(f)}} & {{hpl} \cdot {{coeff}(f)}} \\{{lpl} < {{ep}(f)} < {hpl}} & {{{ep}(f)} \cdot {{coeff}(f)}} \\{else} & 0\end{matrix}\mspace{79mu} \max \left\{ {{gl}(f)} \right\}} = {{{{ep}(f)}{{coeff}(f)}} = {{{{dr}(f)}P_{{maximum},j,{watt}}{{coeff}(f)}\max \left\{ {{nopw}(f)} \right\}} = {{\max {\left\{ {{gl}(f)} \right\}/{{dr}(f)}}} = {P_{{maximum},j,{watt}}{{coeff}(f)}}}}}} \right.}} & \left( {{eq}.\mspace{14mu} 7} \right)\end{matrix}$

Calculation of hpl Using Average Dissipation

FIG. 5 shows hpl being calculated as a function of the averagedissipation ratio within the working band or within the selectedfrequencies. Optionally, this is based on the assumption that a lowaverage dissipation means a high sensitivity and vice versa. Otherfunctions may be used as well, for example, a table matching hpl toaverage dissipation.

As seen in the graph, a low average dissipation ratio indicates a highsensitivity of the load and accordingly dictates a low hpl. The lowvalue of hpl is optionally selected to be slightly above lpl (to providea minimal working range). For example, the minimal hpl value may bebetween 70 and 120 Watts (e.g. 80 Watts). The maximal level of hpl maybe chosen to be as high as the maximal possible amplifier power orslightly below that. As seen in FIG. 5, when the average dissipationratio is below a preset lower limit, hpl is selected to be the lowesthpl allowed, and when the average dissipation ratio is above a presetupper limit, hpl is selected to be the highest hpl allowed. The lowerlimit for average dissipation ratio may be, for example, between 0.1 and0.3 (e.g. 0.2) while the upper limit may be for example between 0.5 and0.9 (e.g. 0.6).

In-between values of average dissipation optionally dictate anintermediate hpl value. It is to be appreciated that while FIG. 5depicts a generally linear correlation for the intermediate averagedissipation ratio values, other functions, optionally non-linear, may beused that provide a positive correlation between the average dissipationratio and hpl (e.g. exponential, step function, polynomial, step-wiselinear).

In some cases, the frequency distribution is in frequency bands, so thatone band can be recognized as matching ice (e.g., low dissipation) andanother matches water (e.g., high dissipation). Optionally, instead orin addition to calculating hpl, gl(f) is set to be zero or at lpl (orany other preset low value) for bands associated with water and at anypreset high value (e.g. hpl or a maximum available power or othersetting) for ice-associated bands. Optionally, the classification ofbands as water/ice is updated optionally periodically based on spectralinformation that is periodically acquired.

While particular ways of calculating hpl and gl(f) are described above,the methods can be combined, for example, arithmetically or logically,for example, using an average value of several methods or using aminimum or maximum or multiple methods. For example—a Gaussian functionof dr(f) (or of dr′(f)) may be used to calculate gl(f).

Exemplary Operation

Attention is now drawn to FIG. 4, which depicts a flowchart 40 showinghow the device 10 may be operated according to an exemplary embodimentof the invention.

Sweep 41 is essentially the same as sweep 21 in FIG. 2. Once one or moresweep results are obtained, decision 42 is performed. At decision 42 adecision is made; namely a selection is made between two or more energytransmission protocols and (optionally) termination of the operationsequence. This decision may comprise one or more of the followingdecisions:

Thawing Protocol—when thawing mode is operated, decision 42 optionallycomprises a selection of frequency/power or frequency/energy pairs thatare expected to dissipate more energy into ice than into water (e.g. asdescribed above). In an exemplary embodiment of the invention, thawingis detected by tracking one or more of the rate of changes in thespectral image (e.g., changes are faster as phases change); thetemperature change rate (e.g., temperatures change faster as phaseschange) and/or the temperature (e.g. with a sensor).

Heating Protocol A—when this mode is operated, decision 42 optionallycomprises a selection of frequency/power or frequency/energy pairs thatare expected to dissipate a different energy pattern by one group offrequencies characterized by a given absolute or relative dr (or dr′)value range than by at least one other group. In an exemplary embodimentof the invention, high power or a larger amount of energy per heatingcycle is dissipated by one group of frequencies (e.g. those having arelatively high dr or dr′ than those having a lower dr or dr′), while inboth groups a non-zero amount of power and energy is dissipated.

Heating Protocol B—in an exemplary embodiment, decision 42 comprises aselection of frequency/power pairs that are expected to dissipate moreenergy into the load than elsewhere (e.g. surface currents, antennamatching, etc.). Non limiting examples for such protocols are disclosedin PCT publications WO07/096,878 and WO08/007,368.

Keep Warm Protocol—in an exemplary embodiment, decision 42 comprises aselection of frequency/power or frequency/energy pairs that are expectedto dissipate an essentially equal amount of energy in all portions ofthe load in a cycle. Optionally, this heating is controlled such thatthe temperature of the object will not deviate significantly from apreset temperature (e.g. 35° C.±2° C. or 45° C.±2° C.). For example,this may be done using feedback from a temperature sensor or by limitingthe energy allowed to dissipate at any given time. It should be notedthat heating water may cause the water to boil away, thereby utilizingdissipated power for evaporation, while other portions may not haveevaporation, causing heating.

Protocol Selection—in an exemplary embodiment the protocol is capable ofautomatically changing operation modes (e.g., terminate thawing oncephase change is complete and/or begin heating at that time or select athawing decision formula). This may depend on input from a sensor and/orfrom information obtained in a frequency sweep, and/or be based oninstructions (e.g. the amount of energy to dissipate in the load at agiven step). The decision might be to terminate operation or to changefrom one protocol (e.g. thawing) to another (e.g. warming).

An example for a sensor input includes the sensing of temperature. Oncethe temperature sensed by one or more of the sensors (or a calculatedtemperature, for example, an average) or the temperature at all sensorshas reached a predefined temperature, the device may decide to changethe heating protocol. For example, if the sensed temperature indicatesthat thawing is completed, the device may change the protocol to eitherstop heating or to begin cooking or to maintenance of the sensedtemperature (e.g., to ensure full thawing and/or preventrecrystallization if a portion of the load is still frozen or tomaintain a load at a serving-ready temperature).

At times, the predetermined temperature that indicates completion ofthawing is slightly above the freezing point (e.g. 2-15° C.). When thesensed temperature is an external temperature of the load (e.g. by useof an IR sensor), the predetermined temperature may be at times beselected to be slightly higher than when using internal sensors (e.g.8-10° C.), since at times, the inner temperature at the end of thawingis lower than the outer temperature (especially if the device provides awarm interior). In another alternative, if the device interior is cool,the inner temperature may be expected to exceed that of the exterior, inwhich case the sensor reading to indicate the termination of thawing mayde lower (e.g. 4-8° C.). At times (e.g., when a plurality of internalsensors is used) a smaller temperature range might be preferred (e.g. 4°C.-6° C.).

Decision 42 may also be based on some form of user input that may beprovided before or during operation. The input may be provided throughone or more of a user interface, and using a machine readable tag, suchas a barcode or RFID. The user input may comprise information regardinga sequence of decisions and/or the triggers thereto, such as one or moreof the amount of energy to dissipate, a phase change, a temperaturechange and/or a temperature change rate.

Once decision 42 is concluded, an energy transmission step 43 at theselected frequency/power or frequency/energy pairs may be transmitted.Optionally, the decision was to terminate operation, in which case thedevice would transmit no energy to the load, and may send notice (e.g.,by playing a sound, light or any form of communication) to a user. Atsuch time the device may terminate operation automatically. This may beaccompanied by notification to the user (e.g., by light, sound ormessage display, or by transmitting an electronic message to a remotedevice for example a cell phone or computer).

Energy transmission 43 may continue for a period of time (predefined orbased on a sensor feedback) and terminate automatically. Optionally oralternatively, transmission 43 is followed by a repeated sweep 41, whichallows adjusting the device's operation to changes that occurred duringheating (e.g. phase change or new spectral information). Optionally oralternatively, operation of the device at each stage may be manuallyterminated by a user.

Additional Exemplary Operation

As noted above, a material may include two or more portions (e.g., 3 ormore) which it may be desirable to heat by different amounts of energyper unit mass (or volume) and/or at different uniformity/efficiencyratios and/or in which different dissipation ratios are observed.Optionally or alternatively, it is possible that most or all of theseportions are not frozen materials or materials that change phase duringheating. For example, a portion of relatively high-fat material may beheated together with a portion of a relatively low fat material and/or aportion of relatively high-water material, or a mixture thereof.

In an exemplary embodiment of the invention, when power is applied to anobject, parts of the object are classified according to theirdissipation ratio and this drives the power (or energy) applicationprotocol used for each such classified portion. It should be noted thatportions may be physically separate or intermingled. In an exemplaryembodiment of the invention, when power is applied to a load, thetransmitted frequencies are classified according to their dissipationratio in the load and this drives the power (or energy) applicationprotocol used for each such classified group of frequencies. It shouldbe noted that at times, at least two different groups of frequencies aretransmitted differently, such that a significant amount of energy isdissipated by all frequencies of said at least two groups.

FIG. 8 is a flowchart of a method of differentially heating materialswith frequencies having different dissipation ratios in the load, inaccordance with an exemplary embodiment of the invention.

At 802, spectral information is optionally acquired. Optionally oralternatively, electro-magnetic properties of portions of an object tobe heated may be input, for example, manually, using a camera or usingan information-bearing tag associated with the object. Alternatively,for example for some protocols such as thawing, frequencies of water andice may be provided ahead of time.

At 804, various “working” frequencies are optionally identified withrespect to them being useful for the intended heating. Optionally oralternatively, it is determined which frequencies to use with thesystem, for example, based on amplifier abilities and/or otherconsiderations, such as not operating at a high Q factor, or atexcessively low dissipation ratios (e.g. 10% or less).

At 806, the dissipation ratio values are optionally normalized, forexample, so that the maximal observed dissipation is given a 100% valueand the minimal observed dissipation ratio is given a 0% value.Normalization is optionally linear, for example as explained in thethawing example above.

At 808, working frequencies are grouped according to their dissipationratio (dr), or normalized dissipation ratio (dr′) and/or heating rate.Optionally, the frequencies are clustered according to thresholds.Optionally, such thresholds are provided as noted above regardinginformation input. Optionally or alternatively, the frequencies areclustered according to their dissipation ratios. Optionally, thedissipation ratio distribution is used to identify an object and/orprovide an indication of its composition and/or material phase.Optionally, additional inputs are used, such as a camera or a weightscale and/or humidity/temperature sensor and/or information providedmanually or by a machined readable tag (e.g. RFID). For example, theremay be 2, 3, 4, 5 or more different dissipation ratio sets identifiedfor associating frequencies therewith. Optionally, the power at one setis at least a factor of 2, 3, 4, 7, 10, 20 or smaller or intermediatefactors of a second set with non-zero transmission. In an exemplaryembodiment of the invention, at least one set, or optionally all setshave a bandwidth of at least 5%, 10%, 20% or smaller or intermediatebandwidth percentages of the total working bandwidth. In an exemplaryembodiment of the invention, at least one set and optionally all setscorrespond to dissipation ratios of a span of at least 5%, 10%, 20% orsmaller or intermediate spans of dissipation ratio values, for example,a set corresponding to a range of between 45% and 55% dissipationratios.

In some cases there is an overlap between ranges of dissipation ratiosassociated with different portion types or locations. At times, a givenfrequency or group of frequency dissipates both in a high dissipationratio portion(s) of a load and a low dissipation ratio portion(s) of aload, such that the frequency displays an intermediate overalldissipation ratio. In some embodiments, frequencies within such overlapsare simply not used. Optionally or alternatively, such frequencies areassigned a separate category. It should be noted that in someembodiments of the invention it is of interest to increase the amount ofpower (or heating) delivered to a particular portion and/or to reducethe number of frequencies used, while possibly reducing homogeneity.This need not interfere with the main goal of differently applying poweror heat to different portions. This can also affect the protocolsapplied to different sets. For example, a protocol may be defined withrespect to the amount of power provided for a set and this power levelmay be distributed among more or fewer frequencies, based, for example,on ease of frequency changing, reliability of the identification of thefrequency in question with a particular portion. Optionally oralternatively, a single set of frequencies of a single portion may bedivided up into multiple sets (and/or combined with another set) for thepurpose of assigning different protocols thereto. This may be useful forproviding desired homogeneity levels and/or heating velocities.Optionally or alternatively, two sets may be combined. Optionally, setsand association of frequencies thereto may change during heating.Optionally, a heating protocol of an object includes points in time toreconsider the association of frequencies into sets.

In some embodiments, the number of groups to which the sets offrequencies is fixed in advance, for example 2-10 groups or 2-4 groupsof frequencies, wherein each group is used to transmit energy to theload at a different heating protocol.

At 810, different power application protocols are associated with eachset. A power application protocols can include, for example, one or moreof: maximum power, minimum power, power relative to other sets or toother frequencies within a set, maximum heating rate, minimum heatingrate, relative heating rate (e.g., between sets or between frequencieswithin sets), power per set, power per each frequency within a set,power to be dissipated in the load by a given set or frequencies withina set, time profile of power application, method of non-maximal powerachievement (e.g., amplification factor, duration at each frequency,number of repetitions in a set and/or combination thereof), heatinghomogeneity vs. velocity tradeoffs, time profile of pauses between powerapplications and/or cycling of power application between frequencies. Adevice may include a memory having stored therein multiple suchprotocols. It should be noted that the protocols may be markedlydifferent, for example, one portion of the food may be thawed, whileanother portion is cooked or baked.

In one example, there is little or no power (or energy) transmission athigher dissipation ratios and optionally homogeneous transmission atlower dissipation ratios. Optionally, for intermediate dissipationratios, there is a discrete decreasing function (optionally a stepfunction at 30% or 50 dissipation ratio), for example, as describedabove for a thawing application.

In another example, one food portion (e.g., food which is less sensitiveto overheating) is heated fast, with maximum power, possibly resultingin more in-homogeneity, while another food portion with otherdissipation characteristics is heated slower and/or to a lowertemperature, and optionally more uniformly.

At 812, the power application protocol is applied. The process may thenbe repeated. In some embodiments, acquiring spectral information and/orassigning profiles need not be applied at every transmission sweepand/or at same frequency. The rate of sweep between heating sessions maybe fixed or it may change during heating, for example as described abovein connection with an exemplary thawing process.

It should be noted that while the above description has describeassociating frequencies into sets, this need not be actually done,rather setting thresholds for different power application protocolsinherently describes such sets and allows the decision of powerapplication protocol to be applied on a frequency by frequency basis. Itshould also be noted that in some cases, the determination of how muchpower to apply and in what protocol, is directed at sets, rather thanindividual frequencies, with a decision regarding frequency/power pairsbeing decided after allocation of power to sets is carried out.

As noted herein, when a power is associated with a frequency, this neednot mean that the power at which energy is transmitted at the frequencymust change. Rather, the power si an aggregate power and can beaffected, for example, by a longer transmission time. Optionally, theactual transmitted power is selected according to an ability of theamplifier of the system, for example, according to a high efficiencypoint of the amplifier or according to a time it takes to changeamplification. It is possible that actual power will depend on themaximum power at any frequency. Optionally or alternatively, a selectionof frequencies to use is made depending on the available amplification,with frequencies with low amplifications optionally avoided.

Example of Multi-Food Heating Experiment

Dissipation properties of some foods and food types are known at variousconditions and frequencies. See for example Bengtsson, N. E. & Risman,P. O. 1971. “Dielectric properties of food at 3 GHz as determined by acavity perturbation technique. II. Measurements on food materials.” J.Microwave Power 6: 107-123. Such known values (for food or any otherload), or using various techniques to estimate or measure thedissipation ratio at different frequencies for a plate (or load)combination, are optionally used to provide differential heating fordifferent objects (e.g., foodstuffs), for example as shown in thefollowing example, which was aimed at controlling the relative heatingof different loads:

Both heating processes were performed using a 900 Watt device with aworking band at 800-1000 MHz, constructed and operated substantiallyaccording to an embodiment of WO07/096,878 ('878);

Cooked rice and raw thigh of chicken were placed together on aconventional household plate and heated according to one of thefollowing protocols:

Protocol 1: Heating is limited to frequencies having a relatively highdissipation ratio, but an essentially uniform energy transfer isperformed in all transmitted frequencies. In this specific protocol, asep(f) normally correlates with the dissipation ratio, transmission of ahomogeneous amount of energy (or power) was performed in the 30% of thefrequencies having the highest ep(f). In addition, transmission wasperformed in all frequencies having at least 80% of the lowest ep(f) ofsaid 30% of the frequencies. It should be noted that also in otherprotocols described herein, the separation of frequencies into setscorresponding to portions may be according to percentage, rather than athreshold.Protocol 2: Maximal transmission is performed at frequencies havingabout 30% or less normalized dissipation ratio (dr′) and no transmissionat frequencies having 80% or more normalized dissipation ratio, with anapproximately linear relation in-between. A graph showing the exactfunction used is attached herewith as FIG. 9.

Temperature was measured before (T₀) and after heating (T₁; ΔT=T₁−T₀).In the chicken, several places were probed, and after heating somevariation of temperatures was observed. In the rice, the temperature wasthe same wherever probed. The results are summarized in the table below:

Plate Protocol composition T₀ (° C.) T₁ (° C.) ΔT 1 100 g chicken 1270-77 58-65 160 g rice 11 47 36 2 105 g chicken 14 66-70 52-56 160 grice 11 72 61

As seen above, in Protocol 1 the chicken heated to a much higher extentthan the rice, while in Protocol 2, heating was more uniform between thetwo foods, with the rice heating slightly more than the chicken. Asimilar result was obtained in repeat experiments. It should be notedthat either result may be desired, depending on the circumstances (e.g.,user preference).

FIG. 10 is a chart showing the normalized dissipation ratio measured inthe device cavity for a rice & chicken plate at different frequencies inthe heating experiment shown for Protocol 2 above. As heatingprogresses, and as the position and/or location of the load changesduring heating, the measured dissipation ratios can change. Nonetheless,a first approximation is that for the higher dissipation ratiofrequencies, most of the energy dissipates in the high dissipation ratioportion of the load (chicken in the instant example) and for the lowerdissipation ratio frequencies, most of the energy dissipates in the lowdissipation ratio portion of the load (in this example—rice).

Thus, when protocol 1 was used, heating was mainly at high dissipationratio frequencies, thereby heating mainly the chicken; when Protocol 2was used, heating was mainly at low dissipation ratio frequencies (butwith a varying amount also in interim dissipation ratio frequencies)thereby heating the rice slightly more than the chicken.

Exemplary Variations

In an exemplary embodiment of the invention, the above methods can beused not only to avoid reaching a certain temperature, but additionallyor alternatively, to minimize a time within a temperature window. Forexample, some temperatures may encourage bacterial growth or fooddegradation if maintained. For example, the above methods may be used toensure that a lower limit of the temperature window is not reached, butis approached, by all the load and then relatively rapid heating applieduntil an upper limit of the temperature window is passed.

While the above have been described as methods of determining a completeirradiation profile, the above methods may also be used otherwise. Forexample, the above hpl calculation may be used as a limit that isapplied after other irradiation profiles are selected, for example, as asafety measure to avoid runaway heating. In another example, frequencybands may be selected to have no power transmitted therein to preventboiling of water, and this selected being applied to an otherwisedetermined method of frequency/power sets.

Optionally, after a portion reaches a target heat and/or is thawed,energy provision is not stopped (or, in some cases, set to lpl), butrather selected to ensure that the portion does not re-crystallizeand/or stays at a desired temperature. As can be apperceived, once it isknown that the portion thawed, a power level that has a desiredtemperature effect on that portion may be calculated form physicalconsideration or using a look up table.

EXAMPLES

The following non-limiting examples illustrate the application of someexemplary embodiments of the invention and should not be taken as beingnecessarily limiting. In the following experiments, a single frozenobject at a time (as detailed below) was placed for defrosting in acavity of an oven having three input antennas within a cylinder shapedcavity, working at 0.9 kW., and spectral information was obtained.

FIG. 6 is a graph showing the spectral information obtained with afrozen (−20° C.) 790 gr cut of bovine sirloin (dashed line) and thespectral information obtained with a frozen (−20° C.) 790 gr portion oftuna fish (solid line). Also shown (dot-dash line) are the averagedissipations calculated from the spectral information, with the averagedissipation for the meat appearing at about 0.5 and the fish at about0.17. The dotted lines depict the maximal and minimal allowed values forhpl (which is typically a function of the device and not the load). Someexamples of places where the dissipation ratio indicates ice, water orice/water are marked.

FIG. 7 shows the spectral information obtained with a frozen (−20° C.)1,250 gr chicken (dashed line) and the spectral information obtainedwith a frozen (−20° C.) 450 gr chicken (solid line). Also shown(dot-dash line) are the average dissipations calculated from thespectral information, with the average dissipation for the largerchicken appearing at about 0.55 and the smaller chicken at about 0.29.

As seen in the graphs, the dissipation at each frequency, as well asaverage dissipation, is affected inter alia by the composition of theload (e.g. meat v. fish, with different fat/protein/water ratios) andits size (with a larger chicken having more liquid water to absorb RFenergy at frequencies where absorption is relatively low).

General

Following is a list of applications and publications describing RF ovensand methods which may be used with the methods and apparatus describedherein:

Title Country Ser. No. DRYING APPARATUS AND METHODS PCT IL2008/000231AND ACCESSORIES FOR USE THEREWITH ELECTROMAGNETIC HEATING PCTIL2007/000235 FOOD PREPARATION PCT IL2007/000864 RF CONTROLLED FREEZINGPCT IL2007/001073 A METHOD AND A SYSTEM FOR A USA 61/064,201 MODULARDEVICE DYNAMIC IMPEDANCE MATCHING IN USA 12/230,431 RF RESONATOR CAVITYELECTROMAGNETIC HEATING USA 12/153,592

In the above description, different frequencies were described as havingdifferent power transmitted there. Such power differentiation can be ofseveral types, including one or more of different peak power, differentduty cycle and/or different rate (e.g., power is supplied at fixamplitudes, but at different rate and/or delays between pulses fordifferent frequencies) and/or at different efficiencies (e.g.,transmitted in a configuration where more power is reflected back to thefeed. In another example, power is provided in sweeps and for each sweeppower is provided at a frequency or not, depending on the total power tobe delivered at that frequency. In another example, power is provided asmulti-frequency pulses, with each pulse including power in a pluralityof frequencies; the frequencies in each pulse and/or amplitude of thepower for a frequency in a pulse may be selected to apply a desiredaverage power.

In general, the term “power” is used to describe the power provided asan average over time (e.g., the time between sweeps).

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

Implementation of the method and/or system of embodiments of theinvention can involve performing or completing selected tasks manually,automatically, or a combination thereof. Moreover, according to actualinstrumentation and equipment of embodiments of the method and/or systemof the invention, several selected tasks could be implemented byhardware, by software or by firmware or by a combination thereof usingan operating system.

For example, hardware for performing selected tasks according toembodiments of the invention could be implemented as a chip or acircuit. As software, selected tasks according to embodiments of theinvention could be implemented as a plurality of software instructionsbeing executed by a computer using any suitable operating system. In anexemplary embodiment of the invention, one or more tasks according toexemplary embodiments of method and/or system as described herein areperformed by a data processor, such as a computing platform forexecuting a plurality of instructions. Optionally, the data processorincludes a volatile memory for storing instructions and/or data and/or anon-volatile storage, for example, a magnetic hard-disk and/or removablemedia, for storing instructions and/or data. Optionally, a networkconnection is provided as well. A display and/or a user input devicesuch as a keyboard or mouse are optionally provided as well.

The word “exemplary” is used herein to mean “serving as an example,instance or illustration”. Any embodiment described as “exemplary” isnot necessarily to be construed as preferred or advantageous over otherembodiments and/or to exclude the incorporation of features from otherembodiments.

The word “optionally” is used herein to mean “is provided in someembodiments and not provided in other embodiments”. Any particularembodiment of the invention may include a plurality of “optional”features unless such features conflict.

As used herein the term “about” refers to ±10.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

As used herein, the singular form “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,the term “a compound” or “at least one compound” may include a pluralityof compounds, including mixtures thereof.

Throughout this application, various embodiments of this invention maybe presented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible subranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed subranges such as from 1 to 3, from 1 to 4, from to 5, from 2to 4, from 2 to 6, from 3 to 6 etc., as well as individual numberswithin that range, for example, 1, 2, 3, 4, 5, and 6. This appliesregardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to includeany cited numeral (fractional or integral) within the indicated range.The phrases “ranging/ranges between” a first indicate number and asecond indicate number and “ranging/ranges from” a first indicate number“to” a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numerals therebetween.

As used herein the term “method” refers to manners, means, techniquesand procedures for accomplishing a given task including, but not limitedto, those manners, means, techniques and procedures either known to, orreadily developed from known manners, means, techniques and proceduresby practitioners of the chemical, pharmacological, biological,biochemical and medical arts.

As used herein, the term “treating” includes abrogating, substantiallyinhibiting, slowing or reversing the progression of a condition,substantially ameliorating clinical or aesthetical symptoms of acondition or substantially preventing the appearance of clinical oraesthetical symptoms of a condition.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention. To the extent thatsection headings are used, they should not be construed as necessarilylimiting.

The present invention has been described using detailed descriptions ofembodiments thereof that are provided by way of example and are notintended to limit the scope of the invention. The described embodimentscomprise different features, not all of which are required in allembodiments of the invention. Some embodiments of the present inventionutilize only some of the features or possible combinations of thefeatures. Variations of embodiments of the present invention that aredescribed and embodiments of the present invention comprising differentcombinations of features noted in the described embodiments will occurto persons of the art.

While the present invention has been described mainly in the context ofthawing, the methods of the present invention, possibly at a higherfrequency, can be used for baking and cooking or any other form ofheating (not limited to kitchens), areas in which conventional microwaveovens are notoriously weak. In one example, when you heat a cheesepastry, the cheese heats faster than the pastry which may be rich inoils and the methods described above may be applied to ensure evenheating. Another example is heating a sandwich with a more dissipatingfilling (e.g., meat, cheese, vegetables), in a manner which heats thesandwich and not the filling (or merely thaws the filling. Otherexamples include a dish of fish and salad (e.g., heat the fish/meat butnot the vegetables) or a dish with meat or fish and rice/pasta (e.g.,heat the rice more than the fish or vice versa, as shown above).

1. A method of heating a load using RF, comprising: (a) providing a loadhaving different dissipation ratios at different portions; (b) settingfrequency/power pairs such that in heating the load a different powerapplication protocol is applied at frequencies that dissipate at a firstdissipation ratio and at frequencies that dissipate at a seconddissipation ratio; and (c) applying said frequency/power pairs to heatsaid load.
 2. A method according to claim 1, wherein said applyingcomprises applying more power for a portion with a lower dissipationratio.
 3. A method according to claim 1, wherein a difference betweentwo or more power application protocols comprises a total amount ofenergy per load amount to be dissipated in their respective loadportions.
 4. A method according to claim 1, wherein a difference betweentwo or more power application protocols comprises a tradeoff betweenheating velocity and homogeneity.
 5. A method according to claim 1,wherein said setting comprises associating frequencies into setsassociated with dissipation ratios; and wherein said setting comprisesselecting frequency/power pairs according to said sets.
 6. A methodaccording to claim 5, wherein said setting comprises selecting a powerlevel per set.
 7. A method according to claim 5, wherein saidassociating comprises associating based on information in addition tosaid dissipation ratio.
 8. A method according to claim 5, wherein atleast one set includes a plurality of non-continuous frequency rangeswith at least one frequency belonging to another set between saidranges.
 9. A method according to claim 5, wherein at least one setcorresponds to frozen material.
 10. A method according to claim 5,wherein associating comprises associating into at least three sets. 11.A method according to claim 5, wherein said associating frequencies intosets is performed by associating into a preset number of sets.
 12. Amethod according to claim 11, wherein said preset number of sets isbetween 2 and 10 sets.
 13. A method according to claim 5, whereinassociating comprises associating into at least two sets each having asignificant amount of dissipated energy or power assigned to a pluralityof frequencies therein, said significant amount being at least 7% of atotal dissipated power in a heating cycle being assigned to a set.
 14. Amethod according to claim 5, wherein at least two of said sets have anon-zero transmitted power and wherein an average dissipated power ofone set is at least twice that of another set.
 15. A method according toclaim 5, wherein at least two of said sets have a non-zero transmittedpower and wherein an average dissipated power of one set is at leastfive times that of another set.
 16. A method according to claim 5,wherein at least two of said sets have a non-zero transmitted power andwherein an average dissipated power of one set is at least ten timesthat of another set.
 17. A method according to claim 5, wherein a set orsets for which power is transmitted cover at least 5% of workingfrequencies.
 18. A method according to claim 5, wherein a set or setsfor which power is transmitted cover at least 20% of workingfrequencies.
 19. A method according to claim 5, wherein at least two ofsaid sets each correspond to a dissipation ratio range of values of atleast 10%.
 20. A method according to claim 1, wherein said loadcomprises food.
 21. A method according to claim 1, wherein said loadcomprises a combination of at least two food portions.
 22. A methodaccording to claim 1, wherein said applying causes a phase change insaid load.
 23. A method according to claim 1, wherein said applyingcauses a thawing of at least a part of said load.
 24. A method accordingto any of claim 1, comprising repeating (b) and (c) at least twice aspart of a heating process.
 25. A method of heating a load using RF,comprising: (a) providing a load having a different rate of heating perpower applied (h/p) at different portions; (b) setting frequency/powerpairs such that in heating the load less power per unit volume ofportions is transmitted at frequencies that correspond to portions witha high h/p rate than at frequencies corresponding to portions with a lowh/p; and (c) applying said frequency power pairs to heat said load. 26.(canceled)
 27. An apparatus configured to perform the method of claim 1,comprising: a cavity; at least one feed configured to transmit RF energyinto the cavity; a controller configured to cause the applying of saidfrequency/power pairs to heat said load according to claim 1; and amemory having a plurality of power application protocols stored thereinand configured to apply different protocols to different sets offrequencies. 28-50. (canceled)
 51. An apparatus configured to performthe method of claim 25, comprising: a cavity; at least one feedconfigured to transmit RF energy into the cavity; a controllerconfigured to cause the applying of said frequency power pairs to heatsaid load according to claim 25; and a memory having a plurality ofpower application protocols stored therein and configured to applydifferent protocols to different sets of frequencies.
 52. An apparatusconfigured to perform the method of claim 5, comprising: a cavity; atleast one feed configured to transmit RF energy into the cavity; acontroller configured to carry out the selecting of frequency/powerpairs according to claim 5; and a memory having a plurality of powerapplication protocols stored therein and configured to apply differentprotocols to different sets of frequencies.
 53. A method according toclaim 5, wherein the applying of the frequency/power pairs to heat theload is performed in accordance with different power levels associatedwith different sets of frequencies.
 54. A method according to claim 5,wherein the applying of the frequency/power pairs to heat the load isperformed by associating time durations with each transmitted set offrequencies.